At the 40th Annual Conference and General Meeting of the Waterbird Society, a symposium and workshop titled Herons of the World Symposium was convened to address the current world status of Ardeidae (herons). This paper introduces the origin of this symposium, demonstrates the geographical areas of study and proposes a framework for future world symposia on coastal and freshwater colonial waterbirds. In that way, it complements the coverage of pelagic colonial waterbirds by the World Seabird Union. The Herons of the World Symposium was held in New Bern, North Carolina, USA, during 21–23 September 2016. The purpose of this first symposium was to bring together heron researchers and enthusiasts from around the world to meet and discuss local, regional and international advances in their biology. In this Special Section, four papers from the symposium are presented. Additional papers and research summaries of participants can be found in the online Journal of Heron Biology and Conservation.

Herons comprise a distinctive family of birds, the Ardeidae, adapted to living in aquatic environments. The history of herons in human culture dates back at least 4,000 years, continuing through successive cultures. Through the millennia, hunting herons for sport, food, or feathers has been one of the more enduring conservation issues for the group. Killing egrets for their feathers initiated the modern conservation era in the United States and Europe. Overall, protection of nesting sites and feeding habitats has been, and remains, a significant theme in heron conservation. Owing to their longevity, wetland dependence, and site specificity, herons have been proposed as potential indicators of environmental conditions and trends. It has been recognized that landscape and regional conservation action is the most effective conservation tool for most species, but several species and populations have been identified as being at risk and requiring special species- and population-level planning and action. To facilitate the conservation of herons, HeronConservation, the Heron Specialist Group of the International Union for Conservation of Nature, was founded in 1982 and has since led global engagement in heron conservation through communication, networking, technical syntheses, and action planning and facilitation.

As heron and egret colonies are sometimes abandoned due to human activity and subsequently newly established at nearby locations, colony locations per se cannot represent colony fates. Here, “colony lineages” were traced by connecting short-distance location shifts between colony sites in consecutive years to quantify the site fidelity of heron colonies themselves rather than the breeding-site fidelity of individuals. Site fidelity of 61 colony lineages recorded from 1963 to 2013 in and around Ibaraki Prefecture, Japan, was evaluated by persistence periods with survival analysis and shapes of historical trajectories by applying the correlated random walk analysis. While 36% (n = 22) of colony lineages did not show site fidelity and lasted only 1 year or indicated untangled shapes of historical trajectories, 64% (n = 39) of colony lineages exhibited site fidelity by reusing the same locations for multiple years or by staying within a small area with entangled shapes of historical trajectories. Even though suitable breeding sites were abundant in the study area and site fidelity of colony members was low, a high rate of site fidelity in colony lineages may be achieved when a few faithful pioneer herons and egrets are followed by many others.

The Great Blue Heron (Ardea herodias) is a Species of Special Concern in the State of Maine, USA, due to declines along the Atlantic coast since the mid-1980s. To determine if this decline was statewide, an aerial survey was conducted from 1 May to 18 June 2015 to estimate the breeding population using a stratified dualframe design accounting for imperfect detection of colonies. The strata were based on habitat and known colony densities. The area frame consisted of 10-km x 10-km plots. Stratum samples were searched by air independently by front and rear observers for known and new colonies. The list frame consisted of plots containing known colonies, a sample of which was checked for nesting activity. The dual-frame design combined the strengths of both list- and area-only surveys. Flying directly to known colonies in the list frame was very efficient, and accounting for new colonies in the area frame, allowed unbiased, statistically valid estimation. Estimates were calculated for a Maine statewide total of active Great Blue Heron colonies (n = 243, 90% credible interval (CI) = 193–352), total nests (n = 2,019, CI = 1,778–2,434), and active nests (n = 1,593, CI = 1,416–1,872). Observer detection ranged from 25 to 99%. The percentage of list frame colony coverage in the dual-frame estimate was 63%, but varied by stratum. The percent CV of the dual-frame statewide total active nests was 8.9%, but also varied by stratum. By repeating these methods, strata and statewide population trends could be obtained.

The Arabian Gulf Coast of Abu Dhabi, United Arab Emirates, consists of highly productive seagrass (Halodule universis, Halophila ovalis and Halophila stripulacea) and mangrove (Avicennia marina) habitats that are essential breeding and non-breeding areas for vast numbers of waterbirds. Due to their dependence on these coastal habitats, waterbirds such as the Western Reef Heron (Egretta gularis) can act as important bioindicators of ecosystem health. The estimated global population size of Western Reef Herons is roughly 10,000 to 100,000 individuals. While populations are currently considered stable, many important breeding and overwintering areas of the Western Reef Heron remain unprotected. Line transect counts were conducted at study sites along the Arabian Gulf Coast of Abu Dhabi monthly throughout 2006-2015. Using a mixed effects model, it was found that both year (F_{1, 1132} = 29.15; P = < 0.001) and month (F_{11, 1132} = 2.32; P = 0. 011) had significant influences on the number of birds counted at any given site; however, there was no statistically significant interaction between year and month (F_11,1132 = 1.24; P = 0.253). While there was an overall non-significant decrease in counts across years (t₄₉₅ = -1.40; P = 0.163), there were significant inverse relationships between year and count at the Al Aryam (t₄₈₅ = -13.55; P = < 0.001) and Abu Al Abyad (t₄₈₅ = -2.23; P = 0.026) sites, suggesting annual relative abundance is declining in these areas. Further research and monitoring of the Abu Dhabi Western Reef Heron population is recommended due to continued destruction and degradation of critical waterbird habitat.

Expanding gull (Laridae) populations throughout the world have been attributed to the availability of anthropogenic food subsidies. The influence of landfills on California Gull (Larus californicus) space use and the timing of their movements was evaluated in San Francisco Bay, California, USA. Using radio telemetry, 108 California Gulls were tracked, > 7,000 locations were recorded, and > 1 million detections were obtained at automated logger systems placed at the two main landfills and three major breeding colonies. Population home range (31-35 km²) and core use areas (2-3 km²) overlapped landfills and colonies, and expanded after breeding. California Gull attendance at landfills (1.6-19.0 km from colonies) increased throughout breeding and post-breeding, whereas attendance at colonies was low during pre-breeding (20%-40% per day), increased during breeding (60%-80% per day), and declined into and during post-breeding (< 20% per day). California Gull attendance at landfills was greatest when garbage was delivered from 06:00 hr in the morning until 18:00 hr at night. In contrast, California Gull attendance at colonies during breeding was greater at night from 20:00 hr to 05:00 hr (50%-70% per hr) than during the day from 06:00 hr to 18:00 hr (30%-40% per hr). Landfills played a predominant role in California Gull space use and the timing of their movements in this highly urbanized estuary.

Very little is known about the numbers and distribution of the Reddish Egret (Egretta rufescens) in western Mexico. To estimate the size and distribution of Reddish Egret colonies along the coast of western Mexico, historical and potential Reddish Egret nesting sites were surveyed in 2008 and 2009. Forty-six colonies were found from Baja California to Chiapas. Mean colony size was 24 pairs/colony (95% CI ± 15; n = 46), but most (74%) colonies were < 20 pairs (Median = 7 pairs; n = 46). The largest colony (258 pairs) and the only two colonies with dark and white morphs were found in Oaxaca. The second largest colony (248 pairs) was found in Baja California Sur. The total breeding population was estimated at 1,108 breeding pairs; 788 pairs in 43 colonies were located in northwestern Mexico (Baja California peninsula, Sonora and Sinaloa, subspecies E. r. dickeyi) and 320 pairs in three colonies were in southern Mexico (Oaxaca and Chiapas, subspecies undetermined). This breeding population, although small, is three to four times larger than previously reported for the Pacific Coast of Mexico (225-300 pairs). Thirty-five (76%) Reddish Egret nesting sites were inside a natural protected area; however, the Oaxaca and Chiapas colonies were not.

Olrog's Gull (Larus atlanticus) is a vulnerable species; however, no study has addressed the relationship between body measurements and sex. To provide an easy and reliable work tool to identify the sex of individuals, adult Olrog's Gulls (n = 111) were weighed, several measurements were taken, and the sexes were determined using DNA analyses. All measurements showed significant differences between sexes, with males being significantly larger (Range = 4.0-15.1%) in all measurements. Logistic regression models were selected using the Akaike information criterion and were validated using leave-one-out cross validation. The best set included three models. Model 1 performed best and included head-bill length, bill depth, wing length and body mass as independent variables, and was closely followed by model 2, which contained the same variables with the exception of wing length. Model 3 included head-bill length, body mass and wing length as independent variables. Model 1 was 1.3 and 2.1 times more likely to be the best model than models 2 and 3, respectively. Model 1 correctly assigned the sex in 94.6% of all birds and 93.4% of females. Model 2 performance was marginally better and correctly assigned the sex in 95.5% of all birds and 95.1% of females. The correct classification of males was 96.0% in both models. Results demonstrate the validity of these measurements, which can be easily taken in the field to reliably determine the sex of Olrog's Gulls.

Hat Island, Lake Michigan, Michigan, USA, is an important historical breeding location for Caspian Terns (Hydroprogne caspia) and other co-nesting species, including Double-crested Cormorants (Phalacrocorax auritus). Although a bird sanctuary of the Michigan Islands National Wildlife Refuge, Double-crested Cormorant management (egg oiling and killing adults) was allowed on Hat Island in 2010; in 2011 and 2012, management actions were restricted to shooting Double-crested Cormorants from at least 500 m offshore. Because the Double-crested Cormorant colony was spread across much of Hat Island, in 2010, a small area of Double-crested Cormorant nests nearest the Caspian Tern colony was left undisturbed to minimize negative impacts on Caspian Terns. Yet, data indicate that management actions had indirect negative impacts on Caspian Terns. Game camera images show that Caspian Terns experienced more frequent disturbances in 2010 as compared to 2011 and 2012. Furthermore, nest inventories and chick banding, in combination with direct chick re-sighting and camera images, show Caspian Tern reproductive success was lower and the colony was abandoned earlier in 2010, as compared to other years. This illustrates that Double-crested Cormorant control actions can cause unintended consequences to co-nesters, even when those conducting management report no impact, and exemplifies that there should be greater consideration of the impacts on co-nesters prior to management.

Satellite and GPS transmitters provide valuable information for bird conservation, though their attachment may have behavioral and/or physical effects. Captive Lesser Adjutant Storks (Leptoptilos javanicus) in Cambodia were divided into a control group (n = 7) and an experimental group (n = 7), and their behavior was monitored during three periods of 22 days each. The experimental group was fitted with dummy backpack transmitters in the second period. Each group included one individual capable of flight (n = 2); all other individuals had the feather vanes of one wing clipped. Both groups interacted by pulling, nibbling or pecking on their own or another bird's transmitter (6.8% of the total interaction time in the experimental group, < 1% in the control group). One individual capable of flight had a skin abrasion when removing the tag, which was likely caused by a tight fit of the backpack rather than its flying ability. The experimental group showed significantly more reflex movements (e.g., sneezing, yawning) in the third period (P = 0.017), but outside factors were assumed to have caused this difference. Despite measurable transmitter effects, no evidence was found that the birds' wellbeing was affected. This study provides a safe transmitter attachment method for Lesser Adjutants that aids future conservation.

To provide an easy and reliable work tool to identify the sex of Rockhopper Penguin (Eudyptes chrysocome) chicks, we weighed and measured 95 nestlings in the crèche phase during 24-31 January 2017 on the Falkland Islands, Argentina. Sex was subsequently determined using DNA analyses of blood from the same individuals. Significant differences were found in bill length (exposed culmen), bill depth and width, flipper length, and diagonal tarsus, but stepwise discriminant analysis showed bill length to be the best predictor for sex determination. Our model correctly classified 82.7% of males and 90.2% of females (overall correct classification 86.2%). Threshold bill length was 36.64 mm, with values above this point being males and values below being females. Therefore, it appears that measuring bill length is an easy, immediate, and accurate method to sex Rockhopper Penguins during the crèche phase.

Mercury concentration was quantified in liver, muscle, and primary feathers of pooled samples of Western Sandpiper (Calidris mauri) collected in December-January 2010 (wintering) and March-April 2011 (premigration) in Ensenada Pabellones and Bahía Santa María, Sinaloa, Mexico, to test for differences between sites, stages, tissues, and age-sex groups. During the winter, mercury concentrations were greater in individuals from Ensenada Pabellones than those from Bahía Santa María (0.81 ± 0.05 vs. 0.57 ± 0.05 mg/kg dry weight, respectively), and greater in liver than in muscle (0.89 ± 0.05 vs. 0.49 ± 0.05mg/kg dry weight, respectively). In the comparison between the stages, wintering birds had greater concentrations of mercury than those of premigration period (0.62 ± 0.05 vs. 0.48 ± 0.05 mg/kg dry weight, respectively). These mercury concentrations were lower than those found in other wintering sites in North America (mean = 4.4 mg/kg dry weight). Although these concentrations suggest that Western Sandpipers wintering on the coast of Sinaloa, Mexico, were being exposed to low mercury concentrations and had not accumulated mercury, it appears that mercury in their tissues decreased during the nonbreeding season. However, these conclusions are based on low numbers in some categories and require further work with individual, rather than pooled, samples.

Anecdotal observations of American Oystercatchers (Haematopus palliatus) destroying Piping Plover (Charadrius melodus) eggs and killing Piping Plover chicks may be limiting Piping Plover productivity. Therefore, 212 focal observations of Piping Plovers and American Oystercatchers were recorded during the 2011 and 2012 breeding seasons at Breezy Point, New York, USA. Thirty agonistic interspecific interactions were observed, almost half (n = 13) of which occurred between Piping Plovers and American Oystercatchers. Piping Plovers initiated significantly more agonistic interactions (76%, n = 13) toward American Oystercatchers than those initiated by American Oystercatchers (8%, n = 13) toward Piping Plovers. All agonistic interactions between Piping Plovers and American Oystercatchers began after one of the species entered the territory of the other. These interactions appear to have a higher potential for fitness reduction in Piping Plovers than American Oystercatchers, and occurred approximately once every 12 hr of observation. Due to the similarity between nesting habitats of Piping Plovers and American Oystercatchers, a plan that focuses on habitat enhancement for beach-nesting birds rather than individual species is recommended.

The influence of an unusual concentration of sea ice and breeding failure on the foraging movement patterns and habitat use of Great Black-backed Gulls (Larus marinus) was investigated. GPS loggers were deployed on three incubating females when multi-year sea ice moved into foraging ranges, dividing the tracking period (1–23 June 2017) into ice-free (5–10 days) and ice-present periods (11–12 days). Foraging trip parameters (e.g., distance, duration) differed among individuals but not with ice conditions. Great Black-backed Gulls decreased use of islands when ice was present (0.05 ± 0.08 locations/trip) relative to absent (5.9 ± 0.5 locations/trip), but increased use of marine habitat when ice was present (9.4 ± 0.2 locations/trip) relative to absent (2.9 ± 0.2 locations/trip). Great Black-backed Gulls also moved at higher speeds in areas of 91–100% ice cover relative to < 50% ice cover, suggesting that low percent cover sea ice acts as important at-sea foraging/roosting sites. Additionally, two Great Black-backed Gulls that were continuously tracked during post-breeding failure repeatedly visited the colony throughout July-August, suggesting some advantage to maintaining a presence at nest sites.

In the last two decades, more than 35% of coastal wetlands in the tropics and subtropics have been destroyed, mangrove forest being the most affected habitat. However, mangroves have been poorly studied around the world, particularly in the Neotropics. The spatio-temporal diversity of the mangrove bird community in the Jambelí archipelago, in southwestern Ecuador, was studied. Between 2 August 2015 and 25 July 2016, a total of 118 species (35 migratory and 83 resident species) belonging to 44 families were documented. Nine of the 83 resident species are endemic to the coasts of Ecuador and northwestern Peru; six are threatened species. The most abundant species in the archipelago were Magnificent Frigatebird (Fregata magnificens) and Neotropic Cormorant (Phalacrocorax brasilianus), while the best represented family was Laridae (n = 12 species). No spatial or temporal differences in bird diversity were detected (P > 0.35). The Jambelí archipelago has a high diversity of bird species, particularly as a wintering and stopover site for boreal migratory species. A long-term monitoring program for bird populations in the area has been proposed as an effective tool to assess the conservation status of this important and threatened ecosystem.